I use the test strips from
Rega, the Taiwan outfit. They come in boxes of 50 so that's the minimum order. I get them as part of a society group order - we buy enough to get a very good price break. They have some distinct advantages - longer shelf life and no refrigeration needed, require a much smaller sample - making them very useful for miniatures and seedlings. Occasional very faint positives that could be false, but also very sensitive so can be used for "group testing" of several plants (so that a negative means they're all clean)